An internal combustion engine equipped with a variable compression ratio mechanism, in which a compression ratio of the internal combustion engine is variably controlled optimally depending on an operating condition of the internal combustion engine for the purpose of improving a thermal efficiency of a reciprocating internal combustion engine and avoiding abnormal combustion such as knocking or the like, is generally known. For example, internal combustion engines equipped with a variable compression ratio mechanism, which is comprised of a multilink piston-crank mechanism, have been disclosed in Patent documents 1 and 2.
The foregoing variable compression ratio mechanism is provided with a plurality of intermediate links through which a piston and a crankshaft are linked together, and a control link for limiting a degree of freedom of these intermediate links. Also provided is an actuator for changing the rotational position of a control shaft. A relative position of the piston can be vertically displaced by changing the rotational position of the control shaft and by moving a fulcrum of oscillating motion of the control link by means of the actuator, thereby changing a compression ratio.
In general, in this sort of variable compression ratio mechanism, for the purpose of preventing a compression ratio from becoming an excessively high compression ratio or an excessively low compression ratio, some kind of stoppers are often provided for restricting movement of the piston-crank mechanism and for mechanically limiting a variable range of the compression ratio.
However, assuming that a motor, serving as an actuator, attempts to further continue to change the compression ratio even after having been restricted by the stopper, for instance owing to a failure (an abnormality) in a controller that controls the motor, an excessive load may be undesirably applied to each component part.